1. Field of the Invention
The present invention relates to an image forming apparatus and a method for inspecting an image.
2. Description of Related Art
Image forming apparatuses are known that form images on sheets based on image data, inspect the formed images, and then detect defects, such as dust, spattering toner, and color deviation in the images (for examples, see Japanese Patent Application Laid-Open Nos. 2005-205706, 2008-15025, and 2007-310567). Sheets having defective images are ejected as waste sheets into a tray different from the tray for sheets having normal images.
A defect of an image is detected at a time of the image inspection usually by determining whether the difference between the original image data and the image data acquired through reading of the sheet surface is beyond a permissible range.
If the sheet having an image formed thereon is not white but is colored or patterned, the difference between the original image data and the read image data is increased due to the color of the sheet. In such a case, a normal image is easily determined to be a defective image erroneously.
Japanese Patent Application Laid-Open No. 2007-310567 discloses a method of preventing false detection of an image defect formed on a sheet having a preprinted image, such as ruled lines. In this method, the image data with its preprinted image (e.g., ruled lines) masked is compared with the original image data to prevent false detection of a defect.
Such a partial mask, however, could not prevent false detection of an image defect if the whole surface of the sheet is colored or patterned.